1. Field of the Invention
The present invention relates to a flow measuring apparatus for measuring an air flow rate and to a construction for mounting the flow measuring apparatus, and particularly relates to an air flow measuring apparatus suitable for measuring a flow rate of intake air drawn in by an engine of an automobile.
2. Description of the Related Art
Air flow rate measuring apparatuses for measuring an air flow rate such as those disclosed in Japanese Patent Laid-Open No. 2001-099688 and Japanese Patent Laid-Open No. 2000-162009, for example, are already known.
A first conventional air flow rate measuring apparatus, disclosed in Japanese Patent Laid-Open No. 2001-099688, is constructed such that a measuring conduit enveloping a flow rate detecting element for measuring an air flow rate and a control circuit portion for outputting a detection signal from this flow rate detecting element are formed into an integrated module. To measure the air flow rate, this first conventional air flow rate measuring apparatus is fixed to an air flow line through which the air being measured flows such that the measuring conduit extends into the air flow line. Moreover, when this first conventional air flow rate measuring apparatus is applied to measurement of the flow rate of intake air drawn into an engine of an automobile, the air flow line may be a duct disposed in an air cleaner or downstream from the air cleaner, for example.
This first conventional air flow rate measuring apparatus is formed into a module in which the measuring conduit is disposed on a lower surface of a base member and the control circuit portion is fixed to an upper surface of the base member. A joint portion is disposed at a boundary between the base member and the measuring conduit. This joint portion is formed with a circular cross section having a small diameter capable of enveloping the cross section of the measuring conduit, and a groove portion for mounting an O ring is recessed into an outer peripheral wall surface of the joint portion. Two mounting apertures are disposed in the base member and the control circuit portion so as to be positioned on mutually opposite sides of the joint portion.
The first conventional air flow rate measuring apparatus is mounted to the air flow line by inserting the measuring conduit through an insertion aperture disposed through a wall surface of the air flow line with the O ring mounted in the groove portion, passing mounting screws through the two mounting apertures, and securely fastening each into threaded apertures of bosses disposed on the air flow line. The O ring is held between the joint portion and the inner wall surface of the insertion aperture, ensuring the airtightness of the air flow line.
A second conventional air flow rate measuring apparatus is disclosed in Japanese Patent Laid-Open No. 2000-162009 in which a metal member formed with grooves and steps is disposed on the base member and the control circuit portion, and protrusions engaging the grooves and steps are disposed on an outer wall surface of the air flow line. It is claimed that when this second conventional air flow rate measuring apparatus is mounted to the air flow line, the grooves and steps of the metal member and the protrusions are made to engage each other, enabling irregularities in assembly to be reduced.
In the first conventional air flow rate measuring apparatus, because the joint portion is formed with a circular cross section and the bosses of the base member and the air flow line are formed on a common plane, the range of rotational movement of this measuring apparatus with the measuring conduit inserted into the insertion aperture of the air flow line is large. Thus, it is difficult to align the positions of the mounting apertures on the measuring apparatus and the threaded apertures of the bosses on the air flow line with the measuring conduit merely inserted into the insertion aperture, making it is necessary to position the mounting apertures and the threaded apertures of the bosses while rotating the first conventional air flow rate measuring apparatus with the measuring conduit inserted before fastening the mounting screws.
Generally, the two mounting screws are fastened on one side at a time. Thus, in cases where the mounting apertures and the threaded apertures of the bosses have been made with dimensional tolerances in mutually opposite directions relative to set values, for example, even if the fastening of one screw is performed, the other screw cannot be fastened, making it necessary to loosen the mounting screw which was fastened first and make fine adjustments to the positions of the mounting apertures and the threaded apertures of the bosses. In other words, it is necessary to fasten the mounting screws twice.
Thus, in the first conventional air flow rate measuring apparatus, one problem has been that insertability into the air flow line and workability of the fastening of the screws have been poor.
In the second conventional air flow rate measuring apparatus, it is necessary to dispose the metal member on the apparatus and machining must be performed to form the grooves and the steps on the metal member, and in addition, protrusions for engaging the grooves and the steps of the metal member must be disposed on the air flow line, etc., placing constraints on manufacture and giving rise to cost increases. Furthermore, if the shapes of the grooves of the metal member and the protrusions on the air flow line are set such that mountability of the second conventional air flow rate measuring apparatus is not lost, the protruding portions may be fine and weak, and there is concern that the protruding portions may be damaged during insertion of the measuring apparatus or during fastening, preventing the desired effects from being achieved.
The present invention aims to solve the above problems and an object of the present invention is to provide an inexpensive air flow rate measuring apparatus having a superior rate of production enabling mountability to an air flow line to be improved by providing a position regulating portion for regulating position relative to an air flow line and enabling flow rate detection precision to be ensured by suppressing rotational assembly irregularities.
With the above object in view, according to a first aspect of the present invention, there is provided an air flow rate measuring apparatus for measuring a rate of air flow flowing inside an air flow line, the air flow rate measuring apparatus being mounted by being fixed to at least two bosses disposed so as to protrude from a wall surface of the air flow line. The air flow rate measuring apparatus includes a measuring conduit disposed inside the air flow line so as to envelop a flow rate detecting element; a circuit portion having a control circuit for outputting a flow rate detection signal, the circuit portion being electrically connected to the flow rate detecting element; and mounting portions for fixing to the bosses. The air flow rate measuring apparatus is characterized in that the measuring conduit, the circuit portion, and the mounting portions are constructed as an integrated part, and a position regulating portion for regulating a mounting position by engaging an outer peripheral surface of each of the bosses is formed on each of the mounting portions.
Therefore, provided is an inexpensive air flow rate measuring apparatus having a superior rate of production enabling mountability to an air flow line to be improved and enabling flow rate detection precision to be ensured by suppressing rotational assembly irregularities.
According to a second aspect of the present invention, there is provided an air flow rate measuring apparatus for measuring a rate of air flow flowing inside an air flow line, the air flow rate measuring apparatus being mounted by being fixed at at least two positions by a boss disposed so as to protrude from a wall surface of the air flow line. The air flow rate measuring apparatus includes a measuring conduit disposed inside the air flow line so as to envelop a flow rate detecting element and a joint portion for ensuring airtightness of the air flow line when the measuring conduit is inserted into the air flow line by engaging an insertion aperture of the air flow line. Also, the air flow rate measuring apparatus includes a circuit portion having a control circuit for outputting a flow rate detection signal, the circuit portion being electrically connected to the flow rate detecting element and a mounting portion for fixing to the boss. The air flow rate measuring apparatus is characterized in that the measuring conduit, the joint portion, the circuit portion, and the mounting portion are constructed as an integrated part, and an outer peripheral surface of the joint portion is formed into a continuous curved surface capable of preventing rotation of the joint portion when inserted into the insertion aperture of the air flow line.
Therefore, provided is an inexpensive air flow rate measuring apparatus having a superior rate of production enabling mountability to an air flow line to be improved and enabling flow rate detection precision to be ensured by suppressing rotational assembly irregularities.